How to add font-face to a child theme (in a text editor)

The first thing you’ll need to do is hook into the TinyMCE font_formats object:
http://www.tinymce.com/wiki.php/Configuration:font_formats
http://www.wpexplorer.com/wordpress-tinymce-tweaks/ (Adding custom fonts)

Next, if you want them to render properly in the dropdown box and inside the content editor; you’ll need to hook a custom stylesheet to the TinyMCE content_css object:
http://www.tinymce.com/wiki.php/Configuration:content_css
http://codex.wordpress.org/Function_Reference/add_editor_style

These can both be filtered using the tiny_mce_before_init filter.
http://codex.wordpress.org/Plugin_API/Filter_Reference/tiny_mce_before_init